This invention relates generally to conserving bandwidth in videotelephony systems, and more specifically to conserving bandwidth in videotelephony systems by using digital zooming and picture-in-picture functionality.
Videotelephony provides symmetric audio and video streaming for an image source across a communications network. The video stream may be compressed using a variety of compression/transmission standards, including: MPEG-4, H.323, H.261 and H.263. These compression standards provide for some conservation of bandwidth, but since videotelephony relies on telephony links that can be limited to 56 Kbs or lower (e.g., cellular) the bandwidth for videotelephony may remain severely constrained in some instances. Constrained bandwidth causes image quality to suffer, often preventing viewers from detecting important visual queues from images displayed in the videotelephony system.
The ability to zoom the image on a videotelephony display can increase the viewer""s ability to see detail, but at the cost of requiring a re-transmission of the newly zoomed image. This re-transmission consumes bandwidth, thereby reducing the available refresh frequency, and thus reducing the quality of the image displayed.
Images in videotelephony systems can be captured using standard pan-tilt-zoom cameras having optical and/or digital zooming capabilities. Once captured, images in videotelephony systems are digitally transmitted from the far-end (i.e., camera-end) to the near-end (i.e., display-end). Certain videotelephony display systems implement picture-in-picture technology, this is often used to view the near-end image as it is being seen by the far-end display of the videotelephony link and visa versa. Using picture-in-picture technology a viewer can track how they are being seen. Re-transmissions based upon re-aiming and re-zooming the cameras in a videotelephony system consume a significant amount of videotelephony bandwidth.
Intel Corporation of Santa Clara, Calif., USA provides videotelephony capabilities through its ProShare(copyright) Video Conferencing Systems. PictureTel Corporation of Andover, Mass., USA has developed the PictureTel 900 Series Collaboration System for video conferencing. Polycom of Milpitas, Calif., USA provides video conferencing solutions for personal, conference room and board room use. Ezenia! Inc. of Burlington, Mass., USA provides video conferencing through its Encounter family of products. These existing systems provide limited zooming and some picture-in-picture functionality, but none conserve bandwidth by providing digital zooming in a videotelephony system using near-end picture-in-picture functionality.
Video screen magnifiers exist to digitally zoom portions of video display (e.g., computer) screens. The Microsoft Magnifier Version 1.0 (Windows 98 Operating System) provides zooming by splitting the screen and displaying a magnified (zoomed) version of the portion of the screen having mouse cursor or keyboard focus. The desired effect is to have the mouse cursor act as a magnifying glass as it moves over portions of the screen. Alternate versions of screen magnifiers have been developed, for example The Bigshot Magnifier (www.bigshotmagnifier.com) will zoom the full display screen or the active window on the display screen. The Screen Loupe Magnification Utility (www.gregorybraun.com) provides a separate floating window that magnifies a viewer defined area under the mouse cursor. These screen magnifiers provide some rudimentary screen zooming, but are not integrated into a videotelephony system, lower screen resolution and do not conserve bandwidth by providing digital zooming in a videotelephony system using picture-in-picture functionality.
Providing an improved videotelephony experience by conserving bandwidth while enhancing various portions of the displayed image has proven to be a difficult problem. The bandwidth constraints of existing videotelephony systems cause quality of service problems and diminish the viewer experience. These problems include poor image quality do to a lack of sufficient bandwidth to handle re-transmissions for zooming, latency in receiving the re-transmission and images that are displayed too small to read important facial and other body expressions.
Accordingly, the present invention improves the quality of service and image display in videotelephony systems by combining digital zooming techniques and picture-in-picture functionality to conserve bandwidth and enhance selected portions of the video display. The present invention defines a portion of the videotelephony image to be zoomed and limits the re-transmission from the videotelephony image source by preventing instructions to zoom the defined portion from being transmitted to the videotelephony image source. Zooming of the defined portion is performed on the near-end by using an interpolation-based digital zooming technique (e.g., spline interpolation) independent of the zooming capabilities of the videotelephony image source. The zoomed portion is then displayed in a window on a viewer""s display screen.
The zoomed portion can be displayed in an in-place window over the defined portion such that the zoomed portion overlaps adjacent non-zoomed portions of the videotelephony image or in a separate floating window on the display screen. The separate window can be a floating window or a fixed/docked window on the display screen. Additionally, a freeze-frame technique can be used to capture (xe2x80x9cfreezexe2x80x9d) the zoomed image such that re-transmission of the image source does not overwrite the zoomed image.
Benefits of the present invention include allowing multiple viewers of a single source image to independently zoom on desired portions of the image without affecting the other viewers. Re-transmission bandwidth is conserved as no additional video stream is sent when viewers zoom because the zooming is done digitally, at the near-end, not by the camera at the far-end. Additionally, because zooming is performed xe2x80x9clocallyxe2x80x9d, on the near-end, viewers using picture-in-picture functionality to track how they are being seen will not be able to detect whether they are being zoomed or not.
This application is related to formerly filed U.S. patent application having Ser. No. 09/537,926, filed Mar. 29, 2000, entitled THROUGHPUT ENHANCED VIDEO COMMUNICATION, which is assigned to the assignee of the present invention, the entire teachings of which are incorporated herein by reference in their entirety.